(455b) Experimental Optimization of Process Parameters for Ammonia Production

Decarbonizing ammonia (NH₃) production is one of the major targets of net zero by 2050, as the industrial synthesis route is responsible for releasing 1.6 tonnes of CO₂ per tonne of NH₃. One pillar of decarbonization is to enhance the process energy efficiency, while drastically reducing the capital costs. A promising route is to replace phase-changing condensation in the Haber-Bosch (HB) synthesis loop with high temperature absorber columns that enable production at lower pressure. Successful demonstration of the reaction-absorption synthesis loop has been reported earlier, in which cheap, abundant metal halide salts were used to selectively absorb NH₃ almost instantly at a wide temperature at lower pressure. Although absorption of ammonia on metal halides is widely investigated for heat pumps, we still know little about their performance in HB loop. The effect of synthesis loop operating conditions on the reaction-absorption process is yet to be studied. In particular, absorption is a cyclic process and induces transient behaviour in continuous operation of reaction-absorption. Optimizing reaction and absorption to maximize the ammonia production rate and purity in the product line is the subject of this presentation.

Using a CaCl₂-based absorber column, we conducted lab-scale tests to optimize the reaction-absorption process parameters and further improve our understanding of RXN-ABS transient behaviour. We evaluated NH₃ production in three different modes: reaction-only, reaction-then-absorption, and reaction-absorption. Reaction-only tests provided accurate measurements of the reaction rates, whereas reaction-then-absorption tests allowed to measure the extent of NH₃ removal from synthesis gas, downstream of the reactor. The reaction and absorption conditions (pressure, temperature, and space velocity) were varied to evaluate reaction and absorption performance in these tests. Later, these optimized conditions were used to evaluate reaction-absorption performance in a transient and cyclic mode. The NH₃ release conditions and absorber cycling were further studied to achieve +95% NH₃ purity downstream of the absorber, upon regeneration.

References:

Nowrin, Fouzia Hasan, and Mahdi Malmali. "Optimizing Reaction-Absorption Process for Lower Pressure Ammonia Production." ACS Sustainable Chemistry & Engineering 10.37 (2022): 12319-12328.

Hrtus, Daniel J., et al. "Achieving+ 95% Ammonia Purity by Optimizing the Absorption and Desorption Conditions of Supported Metal Halides." ACS Sustainable Chemistry & Engineering 10.1 (2021): 204-212.